jedi-vim: jedi-vim causes lag in insert mode

I’m experiencing an irritating lag in insert mode, i.e. it takes a long (up to 0.5 seconds) time for a character to appear after I type it. One of the files I’m having this issue with is ~800 lines of code, so I wouldn’t expect mere size to be the root cause? Removing jedi-vim also removes the lag, so I assume it must have something to do with this plugin. Completely removing my .vimrc doesn’t seem to have any effect. This happens with supertab, autocomplpop, and also when both of them are disabled.

I profiled some of the insert-mode madness like this:

:profile start profile.log
:profile func *
:profile file *
" At this point do slow actions
:profile pause
:noautocmd qall!

and it seems like _vim_exception is being called rather often (given that I only inserted ~80 chars):

FUNCTION  jedi#_vim_exceptions()
Called 313 times
Total time:   0.014491
 Self time:   0.014491

count  total (s)   self (s)
  313              0.002117     let l:result = {}
  313              0.000798     try
  313              0.000745         if a:is_eval
  261              0.002488             let l:result.result = eval(a:str)
  261              0.000370         else
   52              0.002304             execute a:str
   52              0.000199             let l:result.result = ''
   52              0.000060         endif
  313              0.000390     catch
                                    let l:result.exception = v:exception
                                    let l:result.throwpoint = v:throwpoint
                                endtry
  313              0.000692     return l:result

Perhaps this is an issue with vim-jedi interacting with one of my other plugins, so here’s the global summary:

FUNCTIONS SORTED ON TOTAL TIME
count  total (s)   self (s)  function
    1   0.238969   0.000101  <SNR>20_UpdateErrors()
    1   0.231162   0.000322  <SNR>20_CacheErrors()
    2   0.229969   0.000126  SyntaxCheckers_python_GetLocList()
    2   0.229843   0.000092  SyntasticMake()
    2   0.229751   0.011751  SyntasticLocalMake()
    3   0.053375   0.052994  <SNR>39_RunPyflakes()
    1   0.019087             GetPythonIndent()
  313   0.014491             jedi#_vim_exceptions()
    4   0.012549   0.000207  <SNR>20_OSSupportsShellpipeHack()
    2   0.012342   0.000284  <SNR>20_uname()
   56   0.008552             <SNR>25_Highlight_Matching_Pair()
    1   0.007604   0.000098  <SNR>20_RedrawErrors()
    1   0.005281   0.000056  <SNR>20_RefreshSigns()
    1   0.005174   0.005001  <SNR>20_SignErrors()
    1   0.001678   0.000034  <SNR>20_AutoToggleLocList()
    1   0.001599   0.000316  <SNR>20_ShowLocList()
    1   0.000686   0.000206  SyntasticCheckable()
    1   0.000568   0.000492  <SNR>11_LoadFTPlugin()
    1   0.000495   0.000329  <SNR>5_SynSet()
    5   0.000444   0.000387  <SNR>20_FilterLocList()

FUNCTIONS SORTED ON SELF TIME
count  total (s)   self (s)  function
    3   0.053375   0.052994  <SNR>39_RunPyflakes()
    1              0.019087  GetPythonIndent()
  313              0.014491  jedi#_vim_exceptions()
    2   0.229751   0.011751  SyntasticLocalMake()
   56              0.008552  <SNR>25_Highlight_Matching_Pair()
    1   0.005174   0.005001  <SNR>20_SignErrors()
    1   0.000568   0.000492  <SNR>11_LoadFTPlugin()
    5   0.000444   0.000387  <SNR>20_FilterLocList()
    1   0.000495   0.000329  <SNR>5_SynSet()
    1   0.231162   0.000322  <SNR>20_CacheErrors()
    1   0.001599   0.000316  <SNR>20_ShowLocList()
    2   0.012342   0.000284  <SNR>20_uname()
    3              0.000239  <SNR>39_ActivatePyflakesQuickFixWindow()
    1   0.000279   0.000236  <SNR>20_HightlightErrors()
    1              0.000231  <SNR>15_addtomrufs()
    3              0.000216  SyntasticAddToErrors()
    4   0.012549   0.000207  <SNR>20_OSSupportsShellpipeHack()
    1   0.000686   0.000206  SyntasticCheckable()
   13              0.000159  <SNR>20_LocList()
    1   0.000233   0.000147  <SNR>20_LoadChecker()

Any idea where to look or how to debug this?