Thank you for your report. We were not able to investigate this on the engine version you reported, but there have been many version changes to UE4 since this question was first posted. With a new version of the Engine comes new fixes and it is possible that this issue has changed or may no longer occur. Due to timetable of when this issue was first posted, we are marking this post as resolved for tracking purposes.
If you are still experiencing the issue you reported in the current engine version, then please respond to this message with additional information and we will investigate as soon as possible. If you are experiencing a similar, but different issue at this time, please submit a new report for it.
As mentioned, int8 variables are not usable in Blueprints. The only numerical data types that can be used with Blueprints are uint8, int32, and float. Other numerical data types are usable in C++, but will not work with Blueprints.
Unfortunately this is a design limitation of Blueprints, and not a bug.