That's because HDMI really isn't designed to support this sort of thing. It's piggy-backing on to the HDMI signal and encroaches on the safety margin within the eye pattern.
For budget installs I tell clients that it's possible, but they need to set aside around £100. For that I install an IR repeater system where the IR eye (beneath the TV usually) is extended on Cat cable. The solution involves some soldering and careful assembly to avoid killing the IR emitters, but does work reliably for casual day-to-day use.
For "mission critical" applications I go down the route of a full control system, but that's a £1000+ solution, albeit a far slicker and pretty bomb-proof.
There are budget DIY solutions that don't involve complicated re-engineering such as Cat HDMI extenders
LINK but you do have to be very careful about compatibility and the ancillaries used with them.
Common issues are not realising that the cheaper devices often compress the video for transmission which then reduces picture quality; or they don't work with certain sources or displays, or that they don't do 3D. I've also handled calls from DIYers who thought any Cat cable would do, so they bought cheap CCA (copper clad aluminium) cable and then found it broke during installation because it's far more brittle than solid copper cables. CCA cables also have much lower bandwidth so high resolution signals struggle.
Personally I won't waste time on cheap/budget systems for anything. It's just not worth it. Professionally I haven't the time to keep going back to installs to fix issues caused by clients "saving" £20-£30-£50, and from their point of view paying my call-out fee just once more than wipes out the value of what they supposedly saved. I'd recommend the same approach for any DIYer.
If you'll take my advice, then have a chat with the guys at Keene Electronics. They do a range of ready to use kits, some of which just do IR over a single Cat cable.
LINK.
