Copy > Paste between two Macs only works the first time

[Eric1491393340]

Running OS 10.10.5 on an iMac and a MBP. They also both run Synergy 1.7.6. An example of my problem is this: When I copy a URL from Firefox on the iMac, I can then successfully paste it in an email to be sent from the MBP. However, when I copy a second URL, it won't paste into the email body. Instead I have to first paste it into TextEdit on the iMac and then covert that text from Rich to Plain, recopy it and then it will paste into the email on the MBP. Odd behaviour, right? This seems to only apply to text (including URLs) copied from my browsers (Firefox, Chromium, Safari), and regardless of me trying the paste function via the keyboard attached to the iMac, or the right button of my mouse (or control-click). The issue does not replicate with text copied from say Indesign. Do you have a solution?