Motorcycle Questions? Ask a Mechanic.
Does the bike have ABS? If so, you may have an issue in the ABS motor, such as a sticky solenoid valve. This can be a simple flush to fix ($200 or so) or a complete ABS motor replacement ($500 or so).
If you don't have ABS then I'd first flush the front brake master cylinder. It could be a simple as some debris settling into the bore of the master cylinder causing it to stick when not used. If flushing doesn't fix it then a replacement is in order ($150). I'd first suggest simply removing the lever pivot pin to make sure the lever isn't the problem. You can press in on the master cylinder piston while it is removed.
I hope this helps. Please let me know if I can be of further assistance. Thanks, P.J.