How can I change the font for symbols in a formula?

[Uglyface200]

Compare the plus sign with the dots around it (the one I don’t want) to the one before “27a²d” (the actual plus sign of the font I’m using, which I do want; that part isn’t a formula object but normal text). The minus signs and plus or minus are also affected, but at least I can paste those in manually. Even so, it’s an inconvenience.

[oweng]

Refer the part of my answer here that deals with the minus sign and the related bug fdo#49547. Comment #7 provides a workaround by replacing the current OpenSymbol font with an older one (which was included with LO v3.3). Alternatively, you can obtain the thinner plus sign you require by using:

x {"+"} y

…rather than:

x + y