Ok I definitely believe this to be a bug, luckily I found a work around (for Truecount anyway), I used TreeGridSummaryType.Sum and that counts all of the true booleans...
MKMahalakshmi Karthikeyan Syncfusion Team August 24, 2015 01:04 PM UTC
Sorry for the inconvenience caused.
We can also reproduce the issue you have reported. Hence we have logged an issue report regarding this. A support incident has been created under your account to track the status of this requirement. Please log on to our support website to check for further updates.