Getting 200 OK abd 400 bad request on the same req

Question

My Google Drive app checks on start if its settings files(the files are all on Drive) has changed. Thus on every start sends a files.list request to the Google Drive API to get the files metadata. The app has been used for more then 4 months with no suspicious beahaviour from this request. But the last few days a strange thing is happening. The problem is that from time to time(every 1 out of 10-20 starts) the request gets this response

 {
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "invalid",
    "message": "Invalid Value",
    "locationType": "parameter",
    "location": "q"
   }
  ],
  "code": 400,
  "message": "Invalid Value"
 }

In all other cases the request gets an adequate response(200 OK mostly :)). This is very strange because every time the request is the same and the query string( the q parameter) of course is the same i.e.

GET https://www.googleapis.com/drive/v2/files?corpus=DEFAULT&q=(title%3D'%5BClosed+Captions%5D.profile'+or+title%3D'Profiles'+or+title%3D'%5BGeneral%5D.profile'+or+title%3D'%5BTeletext%5D.profile'+or+title%3D'ezt5RoamingSettings.ini'+or+title%3D'ezt5ProjectSettings.ini'+or+title%3D'Project+Templates'+or+title%3D'ezt5IOPresets.ini'+or+title%3D'dicAutoCorrect.xml'+or+title%3D'dicShortForms.xml'+or+title%3D'dicDictionaries.xml')+and+trashed%3Dfalse&fields=items(fileSize%2C+id%2C+title%2C+modifiedDate%2C+md5Checksum%2C+parents(id%2C+isRoot))&key={MY_API_KEY}

Any ideas why is this happening will be much appreciated...