https monitor on GTM over-ridden by bigip monitor?

I have configured a GTM wideip with a pool with 3 members which are LTM-based virtual-servers (on different bigip devices). The server object in the gtm for each ltm has a bigip monitor. The gtm pool has an https monitor.

During my testing, I have ensured the gtm https monitor fails (by blocking the https at a firewall), but the bigip monitor sees the ltm virtuals are up. I am expecting the gtm pool members to be always down, but am finding that once or twice a minute the members are flagged up for a few seconds.

I assume this is because they are flagged up by the bigip monitor, then flagged down by the https monitor. Is this a valid assumption, or is this a bug?